AirPort Extreme Drops Internet seemingly during high downloads.

Hello! I have a 5yr old iMac, a 3yr old iMac and an AirPort Extreme wireless router that's about 4yrs old. Within the last week, after no previous issues, Internet connection is lost for a few minutes. It always reconnects. I've tried restarting and unplugging both modem and router to reset. I called the ISP and they tried to sell me new product saying my AirPort was old and they get worn out. I find this hard to believe. All software is up to date also. Help!